From patchwork Tue Jan 7 20:53:58 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 234302 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 83BC7C3F68F for ; Tue, 7 Jan 2020 21:19:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 571E02072A for ; Tue, 7 Jan 2020 21:19:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578431987; bh=hNWhhKLpEyLjW7HqyBgu6SklEZFnQ74DzmvMpjq06+I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Z60yIivDzlk9Kj548urYcyBd8/S7jJ7hGfuTpEd9ZMBdMP7n5LP3s7uaASGJpHRXe K0Ak+3X4sOCLRGp0z+Q5mc/PbM+bQGxjyelacesUzJ8+tj5Dj9m5FTTA37aSUczIpp Qc3O2d9fU7uxdTty1djJkiNNOGSYK2PsU0S3EMY4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729103AbgAGVEt (ORCPT ); Tue, 7 Jan 2020 16:04:49 -0500 Received: from mail.kernel.org ([198.145.29.99]:49860 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729094AbgAGVEs (ORCPT ); Tue, 7 Jan 2020 16:04:48 -0500 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 459AB208C4; Tue, 7 Jan 2020 21:04:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578431087; bh=hNWhhKLpEyLjW7HqyBgu6SklEZFnQ74DzmvMpjq06+I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YZjJsg5rGXB1y5rDmXzIo88rWTfrG/UwM3e69VdffQt/U5VwKf3Xmkzy3LTuAfZ4C VZF1lRt5vowIr7w1FvyC/XP0JH4tsQEmY0T1LQMDPYal2wGJS65O4HgLoO+Yq95Mde NLmeJQJxo+VKYLgpMKsMySXu9sPqTJKQ1nxTnCqw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Thomas Richter , Vasily Gorbik , Sasha Levin Subject: [PATCH 4.19 028/115] s390/cpum_sf: Adjust sampling interval to avoid hitting sample limits Date: Tue, 7 Jan 2020 21:53:58 +0100 Message-Id: <20200107205300.877535070@linuxfoundation.org> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200107205240.283674026@linuxfoundation.org> References: <20200107205240.283674026@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Thomas Richter [ Upstream commit 39d4a501a9ef55c57b51e3ef07fc2aeed7f30b3b ] Function perf_event_ever_overflow() and perf_event_account_interrupt() are called every time samples are processed by the interrupt handler. However function perf_event_account_interrupt() has checks to avoid being flooded with interrupts (more then 1000 samples are received per task_tick). Samples are then dropped and a PERF_RECORD_THROTTLED is added to the perf data. The perf subsystem limit calculation is: maximum sample frequency := 100000 --> 1 samples per 10 us task_tick = 10ms = 10000us --> 1000 samples per task_tick The work flow is measurement_alert() uses SDBT head and each SBDT points to 511 SDB pages, each with 126 sample entries. After processing 8 SBDs and for each valid sample calling: perf_event_overflow() perf_event_account_interrupts() there is a considerable amount of samples being dropped, especially when the sample frequency is very high and near the 100000 limit. To avoid the high amount of samples being dropped near the end of a task_tick time frame, increment the sampling interval in case of dropped events. The CPU Measurement sampling facility on the s390 supports only intervals, specifiing how many CPU cycles have to be executed before a sample is generated. Increase the interval when the samples being generated hit the task_tick limit. Signed-off-by: Thomas Richter Signed-off-by: Vasily Gorbik Signed-off-by: Sasha Levin --- arch/s390/kernel/perf_cpum_sf.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c index 5c3fd9032b74..0f4957ac81b6 100644 --- a/arch/s390/kernel/perf_cpum_sf.c +++ b/arch/s390/kernel/perf_cpum_sf.c @@ -1273,6 +1273,22 @@ static void hw_perf_event_update(struct perf_event *event, int flush_all) if (sampl_overflow) OVERFLOW_REG(hwc) = DIV_ROUND_UP(OVERFLOW_REG(hwc) + sampl_overflow, 1 + num_sdb); + + /* Perf_event_overflow() and perf_event_account_interrupt() limit + * the interrupt rate to an upper limit. Roughly 1000 samples per + * task tick. + * Hitting this limit results in a large number + * of throttled REF_REPORT_THROTTLE entries and the samples + * are dropped. + * Slightly increase the interval to avoid hitting this limit. + */ + if (event_overflow) { + SAMPL_RATE(hwc) += DIV_ROUND_UP(SAMPL_RATE(hwc), 10); + debug_sprintf_event(sfdbg, 1, "%s: rate adjustment %ld\n", + __func__, + DIV_ROUND_UP(SAMPL_RATE(hwc), 10)); + } + if (sampl_overflow || event_overflow) debug_sprintf_event(sfdbg, 4, "hw_perf_event_update: " "overflow stats: sample=%llu event=%llu\n",